Retrospective Evaluation of the Effect of Heart Rate on Survival in Dogs with Atrial Fibrillation

Abstract

Background: Atrial fibrillation (AF) usually is associated with a rapid ventricular rate. The optimal heart rate (HR) during AF is unknown.

Hypothesis/objectives: Heart rate affects survival in dogs with chronic AF.

Animals: Forty-six dogs with AF and 24-hour ambulatory recordings were evaluated.

Methods: Retrospective study. Holter-derived HR variables were analyzed as follows: mean HR (meanHR, 24-hour average), minimum HR (minHR, 1-minute average), maximum HR (maxHR, 1-minute average). Survival times were recorded from the time of presumed adequate rate control. The primary endpoint was all-cause mortality. Cox proportional hazards analysis identified variables independently associated with survival; Kaplan-Meier survival analysis estimated the median survival time of dogs with meanHR <125 bpm versus ≥125 bpm.

Results: All 46 dogs had structural heart disease; 31 of 46 had congestive heart failure (CHF), 44 of 46 received antiarrhythmic drugs. Of 15 dogs with cardiac death, 14 had CHF. Median time to all-cause death was 524 days (Interquartile range (IQR), 76-1,037 days). MeanHR was 125 bpm (range, 62-203 bpm), minHR was 82 bpm (range, 37-163 bpm), maxHR was 217 bpm (range, 126-307 bpm). These were significantly correlated with all-cause and cardiac-related mortality. For every 10 bpm increase in meanHR, the risk of all-cause mortality increased by 35% (hazard ratio, 1.35; 95% CI, 1.17-1.55; P < 0.001). Median survival time of dogs with meanHR<125 bpm (n = 23) was significantly longer (1,037 days; range, 524-open) than meanHR ≥125 bpm (n = 23; 105 days; range, 67-267 days; P = 0.0012). Mean HR was independently associated with all-cause and cardiovascular mortality (P < 0.003).

Conclusions and clinical importance: Holter-derived meanHR affects survival in dogs with AF. Dogs with meanHR <125 bpm lived longer than those with meanHR ≥ 125 bpm.

Keywords: Electrocardiography; Heart failure; Holter; Rate control; Ventricular rate.

Figure 1

Kaplan‐Meier estimates of survival based on all‐cause mortality in two groups of dogs with AF divided equally based on the median meanHR of <125 bpm (black line, n = 23) or ≥125 bpm (orange line, n = 23). The group with meanHR < 125 bpm (1,037 days, 95% CI, 524‐ n/a) had significantly longer survival time than group with meanHR ≥125 bpm (105 days, 95% CI, 67–267 days).